Streptococcus mutans, a bacterial species commonly found among the oral microbial flora of man and other animals, is widely believed to be a primary etiological agent of dental caries. S. mutans will utilize a number of simple carbohydrates for growth, including the common dietary sugars sucrose, glucose and lactose. Sucrose, in particular, has been linked to the cariogenicity of S. mutans since it is the substrate for an extracellular enzyme which synthesizes a glucan important for adhesion of this organism in the oral cavity. In addition, the ability of this bacterium to ferment a number of sugars with the production of acid is undoubtedly also important in its ability to promote dental decav. In this proposal, we plan to study the biochemical mechanisms by which S. mutans transports sugars, especially glucose and sucrose, via a phosphoenolpyruvate-dependent phosphotransferase system (PTS). Specifically we intend to investigate: 1) The number and nature of enzymes comprising the S. mutans PTS; 2) Propoerties of the membrane-bound, sugar specific PTS transport permeases (Enzymes II) of S. mutans: 3) Methods for solubilization and purification of these Enzymes II, with emphasis on those specific for sucrose and glucose; 4) The catalytic mechanisms of sugar transport and phosphorylation by the S. mutans PTS. These studies will be important in understanding theoverall physiology of sugar transport and metabolism in oral streptococci and will contribute information relating to structural, functional and evolutionary relationships among the various bacterial phosphotransferase systems.